Glucose metabolism in pregnancy at high altitude.

OBJECTIVE To assess insulin sensitivity and beta-cell function associated with lower maternal fasting plasma glucose levels at high altitude compared with sea level. RESEARCH DESIGN AND METHODS We studied 215 pregnant women at 8-42 weeks of gestation in Peru. The women were recruited from Cerro de Pasco, which is situated 4,370 m (14,340 feet) above sea level, and Lima, which is at sea level. We also examined 53 nonpregnant control subjects (22 in Cerro de Pasco and 31 in Lima). Fasting plasma glucose, insulin, C-peptide, and proinsulin concentrations were measured in samples obtained from the antecubital vein between 8:00 a.m. and 10:00 a.m. after an overnight period of fasting for 10-14 h Insulin resistance and beta-cell function were calculated using homeostasis model assessment. RESULTS Fasting C-peptide levels and beta-cell function were similar, fasting concentrations of insulin and proinsulin were lower, and insulin sensitivity was higher at high altitude compared with sea level. CONCLUSIONS Maternal fasting plasma glucose that is lower at high altitude than at sea level in the presence of similar insulin secretion is associated with higher peripheral insulin sensitivity. This may partly explain the lower birth weights at high altitudes.